The fabrication of semiconductor devices, such as logic and memory devices, typically includes processing a semiconductor device using a large number of semiconductor fabrication processes to form various features and multiple levels of the semiconductor devices. Some fabrication processes utilize photomasks/reticles to print features on a semiconductor device such as a wafer. As semiconductor devices become smaller and smaller, it becomes critical to develop enhanced inspection and review devices and procedures to increase the resolution, speed, and throughput of wafer and photomask/reticle inspection processes.
One inspection technology includes electron beam based inspection such as scanning electron microscopy (SEM). In some instances, scanning electron microscopy is performed via an SEM system which includes an increased number of electron-optical columns (e.g. a multi-column SEM system). In other instances, scanning electron microscopy is performed via secondary electron beam collection (e.g. a secondary electron (SE) imaging system). In other instances, scanning electron microscopy is performed by splitting a single electron beam into numerous beams and utilizing a single electron-optical column to individually tune and scan the numerous beams (e.g. a multi-beam SEM system).
Splitting the single electron beam into numerous beams for a multi-beam SEM system traditionally requires an array of aperture lenses and/or micro-lenses. The array of aperture lenses and/or micro-lenses are set in small, electrically-charged apertures (e.g. less than 100 μm in diameter) that are substantially round in design to create lens fields. If the apertures are out-of-round, astigmatism is introduced in the lens fields which results in a distorted image plane.
Therefore, it would be advantageous to provide a system that cures the shortcomings described above.